1. Technical Field
The invention relates to a heat-sensitive transfer recording medium for use in heat-sensitive transfer-type printers, a producing method thereof, and a heat-sensitive transfer recording method, and more particularly, to a heat-sensitive transfer recording medium wherein a heat-resistant lubricating layer is provided on one surface of a base material, and an undercoating layer and a dye layer are successively formed on the other surface of the base material, its producing method, and a heat-sensitive transfer recording method.
2. Technical Background
Generally, a heat-sensitive transfer recording medium called a thermal ribbon refers to an ink ribbon used in heat-sensitive transfer-type printers, and is provided with a heat-sensitive transfer layer on one surface of a base material and also with a heat-resistant lubricating layer (a back coat layer) on the other surface of the base material. Here, the heat-sensitive transfer layer is a layer of an ink which is sublimated (sublimation transfer type) or melted (melting transfer type) by application of heat generated from a thermal head of a printer to allow transfer to a transfer object side.
The sublimation transfer type system among the heat-sensitive transfer type systems has now been widely applied to self-service printing for digital cameras, cards such as an identification card, output objects for amusements and so on. This is because of the capability of forming various images in full color along with the availability of high-performance printers. With such a diversity of uses, demands for downsizing, speed-up, reduction in cost, or durability of printed objects to be obtained are growing. In recent years, a heat-sensitive transfer recording medium having a plurality of heat-sensitive transfer layers wherein a plurality of protect layers etc. for giving durability to a printed object are provided on the same side of a base sheet so as not to overlap has been in use.
In this surroundings, as printing speed of printers increases along with diversification of uses and increases in popularity, a problem has arisen in that sufficient printing density cannot be obtained with conventional heat-sensitive transfer recording media. Therefore, in order to increase performance, including transfer sensitivity, an attempt has been made to increase transfer sensitivity in the course of printing by thinning a heat-sensitive transfer recording medium. Nevertheless, problems are involved in that wrinkles are caused to occur by the action of heat or pressure etc., during the fabrication of heat-sensitive transfer recording media or during printing, or breakages may occur in some cases.
In addition, an attempt has been made to improve a printing density or transfer sensitivity during printing by increasing a ratio of dye/resin (dye/binder) in a dye layer of a heat-sensitive transfer recording medium. To increase the dye causes not only increases in cost, but also the transfer (offset) part of a dye to a heat-resistant lubricating layer of a heat-sensitive transfer recording medium during the course of winding in a fabrication step and then to re-transfer (re-offset) the once transferred dye to a dye layer of other color or a protective layer during subsequent re-winding. If this contaminated layer is thermally transferred to an object to be transferred thereto, a hue different from an intended color may appear, or so-called scumming may occur.
Further, an attempt has been made to increase in power not only at a heat-sensitive transfer recording medium side, but also at the time of image formation at a printer side. However, this causes not only an increase in power consumption, but also a shortage of life of a thermal head of the printer, along with a tendency that there occurs so-called abnormal transfer, in which a dye layer and an object to be transferred thereto are fused together. In order to prevent the abnormal transfer, if a large amount of a release agent is added to the dye layer or the object to be transferred thereto, image bleeding or scumming occurs.
For solving these demands, for example, in Patent Literature 1, there has been proposed a thermal transfer sheet having, between a base material and a dye layer, an adhesion layer (an undercoating layer) containing a polyvinylpyrrolidone resin and a modified polyvinylpyrrolidone resin.
Further, Patent Literature 2 has proposed, in order to solve not only the problem of a lack of transfer sensitivity, but also the problem of local matting on a print surface, a thermal transfer sheet having an undercoating layer consisting of a copolymer resin of vinylpyrrolidone and vinyl acetate and ultrafine particles of a colloidal inorganic pigment.
As transfer sensitivity increases like this, the dye layer can be made thinner and the total amount of dyes reduces, thus leading to cost reduction. Nevertheless, problems are involved in that a print failure occurs by means of heat or pressure etc., upon printing on the heat-sensitive transfer recording medium or breakage occurs in some cases.
In case where the lubricity of a heat-resistant lubricating layer is insufficient, the wrinkles occurring during the printing on a heat-sensitive transfer recording medium may be caused through the sticking between a base material and a thermal head. In addition, if there is a significant difference between the lubricities of a heat-resistant lubricating layer at low-power printing and at high-power printing, e.g. in case where there are both a print area and a non-print area on the same image, the sticking may occur caused by a difference in friction between the thermal head and the heat-resistant lubricating layer at both areas. Hence, as the dye layer is made thinner, the heat-sensitive transfer recording medium is demanded to have, especially, a high heat resistance.
To solve these problems, Patent Literature 3 has proposed a method wherein a metallic soap and a filler are added to a heat-resistant lubricating layer along with a silicone modified resin to improve lubricity at the time of high-energy printing to prevent the occurrence of wrinkles during printing.